FIG. 1 is a representation of a blown film extrusion line. The extrusion line represented in FIG. 1 includes an extruder 10 that compacts and melts plastic pellets to form a hot, continuous, viscous plastic liquid. The extruder forces the viscus plastic liquid into an annular die 12. The plastic liquid is extruded from the annular die 12 as a thin walled tubular plastic bubble 14. The bubble 14 is pulled vertically upwardly from the annular die 12 by nip rolls (not shown).
As the tubular bubble 14 is pulled upwardly by the nip rolls, the bubble 14 passes through guides 16. The guides 16 engage in contact around the tubular bubble 14 and center and stabilize the bubble. By keeping the bubble 14 centered between the die 12 and the collapsing frame to be described, the gauge of the bubble can be controlled.
After leaving the bubble guide 16 the tubular bubble 14 is continued to be pulled upwardly by the nip rolls into the collapsing frame 18. The collapsing frame 18 is comprised of opposing panels 20, 22 of slats, rollers, panels or wear strips. The opposing panels 20, 22 are angled toward each other as they extend upwardly. The opposing panels 20, 22 engage against the opposite sides of the tubular bubble 14 as it is pulled upwardly between the panels. The panels 20, 22 begin the flattening and collapsing of the tubular bubble 14.
After leaving the collapsing frame 18 the tubular bubble 14 next passes through the nip rolls and is flattened. After the bubble 14 is flattened, it is redirected to other portions of the blown film extrusion line. This is accomplished by turning bars 24, 26. The turning bars 24, 26 are used where a turn in the direction of the flattened bubble 14 is required, together with some adjustment of the bubble alignment. The turning bars 24, 26 are installed at an angle to both the infeed and outfeed directions of the flattened bubble 14. The flattened bubble 14 wraps itself around the surface of the turning bars 24, 26 and leaves the bars at a right angle to the infeed direction of the bubble 14.
In a conventional blown film extrusion apparatus, after leaving the turning bars 24, 26 the flattened tubular bubble 14 would then be directed to other components of the extrusion line by idler rollers.
The blown film process is a very dirty process that leaves a sticky build up of very small particulate residue on the surfaces of the idler rollers and the bearings supporting the rollers. The build up of the particulate residue requires that all the rotating idler rollers and their bearings in the extrusion line be cleaned periodically to remove the residue from the roller surfaces and the roller bearings. It is not unusual for the build up of particulate residue in the roller bearings to cause the idler rollers to stop turning due to the resistance in the bearings caused by the build up of the residue. Furthermore, because the idler rollers become contaminated with the particulate residue at different rates in conventional blown film extrusion lines it is often not possible to tell which idler roller in the line has stopped turning and is creating resistance to the blown film moving through the line. Once an idler roller stops turning, the friction and wear of the blown film tube sliding over the stopped roller increases dramatically, leading to quality and/or production issues.